Patch 0.7.12, under other changes and improvements, bullet point #6:
Fixed a rare bug which disabled the bonus to shell dispersion when guns were locked onto a target.
Let's hope that's the last of it. Though I kind of wonder exactly how rare this bug is/was because I seem to have been experiencing it more regularily than what I'd classify as rare and I can speak for multiple clanmates of mine who had the same experience.
Anyhow, here's to hoping!