Single disk mirror + spare causes lockup :-(

[Piete Brooks]

[ raidtools-19990309-0.90, Linux 2.2.2 + raid0145-19990309 ]

If I create a single disk mirror, then raidhotadd a second disk, it tries to 
resync, but gets nowhere, blocks all other md re-sync's, make the load average 
make the machine look busy (it is actually idle), and means that any "sync" 
operations of the machine wedge.

I now get the idea that I should not do this, but could it fail somewhat more 
gracefully ?