Screensaver gets triggered when mouse is locked

I’m having this problem with DOSBox that I previously didn’t have. Whenever I lock the mouse in the application and play/use DOSBox as usual, the screensaver keeps popping up, no matter how much I move the mouse or type on the keyboard. However when I set DOSBox to not lock my mouse that doesn’t happen. I’ve contacted the DOSBox devs and they pointed out that it might be a SDL issue, so I came here to ask.

$ xset -q
Screen Saver:
prefer blanking: yes allow exposures: yes
timeout: 600 cycle: 600
DPMS (Energy Star):
Standby: 600 Suspend: 1200 Off: 0
DPMS is Enabled
Monitor is On
$ apt-cache policy libsdl1.2debian
Installed: 1.2.15-10
Candidate: 1.2.15-10
Version table:
1.2.15-10 0
500 sid/main i386 Packages
*** 1.2.15-10 0
100 /var/lib/dpkg/status

I’m using CrunchBang 11 with Debian unstrable repos.