Can't drag and drop Product Variations anymore

I posted a similar bug against The Bulk Discounts plugin (see https://www.ads-software.com/support/topic/cant-enable-bulk-discount-on-product-page-with-many-variations?replies=2#post-6891939).

Here is how I reproduced the problem on my test site (running WP 4.2.1;
Virtue theme 2.4.7, WC 2.3.8 and no other plugins running):

created a variable product with 3 attributes:
-attribute1, 7 values
-attribute2, 2 values
-attribute3, 3 values
for a total of 42 combinations

Did a “link all variations” to create 42 variations and did an update to save everything. Then tried to drag the top variation to the bottom of the list and clicked update. The move did not stick; the variant remained where it was before the move.

Through trial and error I found that by removing 5 of the 42 variations, drag and drop of variations worked properly.

Then I did a “link all variations” to add in the 5 variations I had removed. The issue reappeared. Only by removing 5 variations again would it resume working.

https://www.ads-software.com/plugins/woocommerce/