Totally weird trading pattern today - anyone able to...

Totally weird trading pattern today - anyone able to explain?
Five consecutive sets of trades like this - decreasing amounts, all at exactly the same time, all at mid-price, all CXA:

	12:23:48 PM	0.2325	3	0.6975	CXA	CX
1	12:23:48 PM	0.2325	3	0.6975	CXA	CX
2	12:23:48 PM	0.2325	4	0.93	CXA	CX
3	12:23:48 PM	0.2325	6	1.395	CXA	CX
4	12:23:48 PM	0.2325	9	2.0925	CXA	CX
5	12:23:48 PM	0.2325	14	3.255	CXA	CX
6	12:23:48 PM	0.2325	22	5.115	CXA	CX
7	12:23:48 PM	0.2325	33	7.6725	CXA	CX
8	12:23:48 PM	0.2325	52	12.09	CXA	CX
9	12:23:48 PM	0.2325	80	18.6	CXA	CX
10	12:23:48 PM	0.2325	72	16.74	CXA	CX
11	12:23:48 PM	0.2325	51	11.8575	CXA	CX
12	12:23:48 PM	0.2325	189	43.9425	CXA	CX
13	12:23:48 PM	0.2325	290	67.425	CXA	CX
14	12:23:48 PM	0.2325	446	103.695	CXA	CX
15	12:23:48 PM	0.2325	687	159.7275	CXA	CX
16	12:23:48 PM	0.2325	1057	245.7525	CXA	CX
17	12:23:48 PM	0.2325	1626	378.045	CXA	CX
18	12:23:48 PM	0.2325	2500	581.25	CXA	CX