Bug: Staff bracket - does not attach properly between bottom 2 staves of 8-voice score

I'm doing an 8-part choral score (SSAATTBB). Trying to apply a bracket to the 2 bass staves, analogous to brackets applied to each of the other pairs of staves (SS, AA, TT). When extending the bracket first applied to Bass 1 down to Bass 2, upon releasing the bracket flips up and attaches to the S1 staff instead of the Bass 2 staff.

The attached image file shows where the bracket winds up -- look closely for the blue line to the left of the score that extends from Bass 1 up to the bottom of Soprano 1