Non-consecutive item id when importing data

When importing data from an ods spreadsheet (with csvimport), Omeka S affects non-consecutive item id to new items.

There is a gap every 20 items (which matches the configuration of csvimport batch import).

Here is an export after importation:

	o:id
1	8288
2	8289
3	8290
4	8291
5	8292
6	8293
7	8294
8	8295
9	8296
10	8297
11	8298
12	8299
13	8300
14	8301
15	8302
16	8303
17	8304
18	8305
19	8306
20	8307
21	8328
22	8329
23	8330
24	8331
25	8332
26	8333
27	8334
28	8335
29	8336
30	8337
31	8338
32	8339
33	8340
34	8341
35	8342
36	8343
37	8344
38	8345
39	8346
40	8347
41	8368
42	8369
43	8370
44	8371
45	8372
46	8373
47	8374
48	8375
49	8376
50	8377
51	8378
52	8379
53	8380
54	8381
55	8382
56	8383
57	8384
58	8385
59	8386
60	8387
61	8408
62	8409
63	8410
64	8411
65	8412
66	8413
67	8414
68	8415
69	8416
70	8417
71	8418
72	8419
73	8420
74	8421
75	8422
76	8423
77	8424
78	8425
79	8426

I am just curious why?

P-S : This install is still in 2.1.0 Omeka S version. Bug (is any) may be fixed already.
PP-S : Pdf files are imported in the same time with the help of sideload module.

I figured out it is the pdf importation with sideload. Media creations are incremented with the same counter than item one.

Yes, all resources in Omeka S share the same unified ID counter. So there will quite commonly be gaps.

A way to keep the series is to import only the metadata of the items, then to import the images in a second spreadsheet.