I'm having the same problem, except, it wasn't the fixers's texture I changed; it was the bar texture; the Oxford bar. In fact, I changed it multiple times, but the last time I did, the fixers and barman disappeared, though I can click on them. I'm using jpg, so it's not an issue of alpha channel.
This is a bit OT, but, the wiki description of .spr format is written in Aramean on papyrus; I mean, it's pretty old; VS version 4.0, says there. In the current century's spr's, there's something following the texture filename, which is sometimes true, sometimes zero, so I'm not sure if it's boolean or numeric

; but I'm damn sure I've no idea what it's for.
Most importantly, it doesn't mention what I've just learned, namely that the python code that summons the spr can provide additional offsets; so, to get my precisely calculated values for the spr's to actually work (7 decimal places, --to try and get texels to line up exactly dead on screen pixels at 1280 rez, without interpolation artifacts), I guess I'll have to go looking for python code invoking them, and nulling those pesky offsets. :-/ (Ahh, the ironies of abstraction...)