I recently found that the Bloomington Drosophila Stock Center distributed a stock (1197) for roughly 27 years with a misidentified mutation. The stock was listed as carrying Df(4)38, but it likely carried the btl-f mutation instead. I'd like to document the history in case people have used stock 1197 and have been puzzled by their experimental results.
Hochman et al. (1964; FBrf0016176) described the isolation of lethal mutations on the fourth chromosome. These mutations were numbered then placed into numbered complementation groups. Lethal 38 was a member of complementation group 2. The numbered mutations were subsequently assigned lettered allele symbols. Mutation 38 became l(4)2f. These authors found that mutations in complementation group 2 failed to complement the recessive lethality of the btD mutation.
Ayme-Southgate et al. (1995; FBrf0079869) determined molecularly that complementation group 2 mutations were in the same transcription unit as the btD mutation and renamed the l(4)2 alleles as bt alleles with l(4)2f becoming btl-f.
Hochman (1971; FBrf0022724) isolated a deficiency following X-ray mutagenesis that failed to complement three complementation groups located in a distal region of chromosome 4. He called this deletion "lethal factor 38" or lf(4)38, but it was later renamed Df(4)38. The three complementation groups uncovered by this deficiency did not include bt. In other words, Df(4)38 was unrelated to l(4)2f (mutation 38) from Hochman et al. (1964; FBrf0016176).
When stocks from the Mid-America Drosophila Stock Center at Bowling Green State University were transferred to Bloomington in 1997, we received a stock with Bowling Green stock number 2728 that was labeled "ciD spapol/Df(4)38". We began distributing it as stock 1197 with the genotype Df(4)38/In(4)ciD, ciD panciD svspa-pol.
As part of my recent work with the Fourth Chromosome Resource Project, I wanted to use Df(4)38 in complementation tests with new fourth chromosome mutations. I found that deficiencies for genes that should have been deleted by Df(4)38 complemented the fourth chromosome in stock 1197-indicating that no deficiency for that distal region was present in stock 1197.  By happenstance, I also set up a cross with a bt allele and saw noncomplementation - suggesting the presence of a bt mutation in 1197.
Documents from Bowling Green indicated that their stock 2728 had once been distributed with the genotype ciD spapol/l(4)38N. This l(4)38 genotype was changed to the Df(4)38 genotype sometime between 1990 and 1997. I have not found the "N" designation in any of Hochman's publications, so I do not understand its significance.
I have now shown that the fourth chromosome in stock 1197 fails to complement btl-b and btl-k and deficiencies removing bt (Df(4)O2, Df(4)C3 and Df(4)J2), but complements mutations and deletions affecting genes near bt (eyA, eyB, gwCR70482-TG4.0, unc-13E, Df(4)ED6380, Df(4)8-M318, Df(4)8-M91, Df(4)8-M167 and Df(4)8-M175). These results and the historical record are consistent with stock 1197 having the genotype btl-f/In(4)ciD, ciD panciD svspa-pol, but I can't rule out the possibility that the bt mutation in stock 1197 is a different bt allele.
Given that uncertainty and the fact that Bloomington has other stocks with better-characterized bt alleles, we decided to discard stock 1197. Stock 106243 at the Kyoto Stock Center was derived from Bloomington stock 1197, so it is not a bona fide Df(4)38 stock. To my knowledge, no valid Df(4)38 stock exists.