Windows 10, GTX980Ti, 6700k
Broken: 2.79.5 2018-19 02:00 51f14cfa43e
Short description of error
Particle system->Hair->Children->Use Clump Noise is going nuts.
Enabling it and disabling causes completely different results each time, but the problem is that sometimes it completely changes hair look (length). See screenshots attached.
Exact steps for others to reproduce the error
On the attached .blend just keep clicking "Use clump noise", or keep it enabled and change something else, such as "use clump curve".
Clump noise disabled
Look at bear's right arm - the clump noise has been applied there in sort-of OK way. Length was changed minimally.
This one looks quite bad. But had worse.
The slightest change in hair can cause enormous inconsistency between renders. One render - bear is nicely 'trimmed', and one minute later half of the bear looks like Lady Gaga's bad hair day. The change in hair can be impossible to notice by human eye, but it affects clump noise in such random ways that render result is just unpredictable.
Changing noise size value does not help.